1. Field of the Invention
The present invention relates to a novel lighting device being able to produce a uniform surface light with an ultra thin format and a method for manufacturing the lighting device.
2. Descriptions of the Related Art
Typical LED packaging comprises attaching an LED die onto a lead frame made of injected aluminum piece, wire bonding to electrically connect LED to the lead frame, and encapsulating the LED, wire bonds and lead frame with an optical clear epoxy using a molding process, where two leads come out of the molded encapsulant for electrical connection. This type of LED packaging structure produces a “dot” light source and is widely adapted for general lighting, message board and light box. Another type of LED packaging, where the LED is packaged into a very compact format used for SMT assembly, is widely used for LCD backlight unit applications. However, it is well known in the field that these typical LED packaging are costly (as compared to a LED bare die) and cannot be used to create an uniform surface light without a sophisticated optical design and costly manufacturing processes. Taking an LCD device for example, the LCD device comprises key components such as the liquid crystal panel, TFT backplane and backlight module. The individual pixels on the liquid crystal panel are controlled by the TFT backplane to allow the light to pass through to determine the bright or dark state of each pixel under the illumination of light emitted from the backlight module. Due to the trend of thinner displays, the thickness and the cost of backlight modules turn into the main technical point in this field.
There are various kinds of light sources being used in the backlight module, for example, cold cathode fluorescent light (CCFL), electroluminescent (EL), light emitting diode (LED), organic LED (OLED), polymer LED (PLED). In consideration of cost and maturity, an LED array formed by a plurality of light-emitting diodes (LEDs) is commonly used as a light source of a backlight module. Generally, the backlight module can be categorized into: a direct-type backlight module and an edge-type backlight module.
The edge-type backlight modules are widely adopted in LCDs featuring a thin format. The edge-type backlight module comprises a light guide plate and the LEDs are disposed along the peripheral of the light guide plate, where the LED light traveling into the light guide plate and to light up the display. However, it is know in the field that a large-scale light guide plate faces manufacturing difficulty and is costly to be utilized in a large-scale display. Moreover, because light emitted from each LED spreads out through the entire light guide plate, no regional on/off control can be established. Therefore the edge-type backlight module cannot be used for LCD requiring local dimming features.
The conventional direct-type backlight module used for a display directly has the LEDs disposed under the display panel. To enhance the uniformity, a diffuser which is disposed in front of the LEDs is needed. In spite of the direct-type backlight module being suitable for the large-scale displays, it can be well imagined that the direct-type backlight module is not only too complicated to arrange the light sources onto the bezel but also too thick since the diffuser for scattering light has to be spaced apart from the LEDs. In other words, the direct-type backlight module faces a dilemma to provide a uniform brightness or to a thinner appearance.
Given the above, a novel lighting device for large size product manufacturing, ultra-thin format, and uniform surface light and local dimming features needs to be developed for LCD backlight module application.